During operation, internal combustion engines generate various combustion by-products that are emitted from the engine in an exhaust stream. Various approaches may be utilized in order to reduce regulated emissions. In some examples, particulate emissions may be reduced by employing an aftertreatment system with a device such as a particulate filter in an exhaust passage of the engine. Turbochargers may also be used in an engine system to increase a pressure of air supplied to the engine for combustion. In one example, the turbocharger includes a turbine coupled to an exhaust passage of the engine, with the turbine at least partially driving a compressor via a shaft to increase the intake air pressure.
Over time, a particulate load of the particulate filter may increase such that regeneration of the particulate filter is required. Regeneration serves to clean the particulate filter and thereby avoid an undesirable increase in backpressure on the engine, for example. One approach to cleaning the particulate filter involves raising the temperature of the exhaust upstream of the filter to promote the burning of carbonaceous particles that have accumulated in the filter. In one example, raising the exhaust temperature may be achieved through active regeneration of the filter by injecting hydrocarbons, such as fuel, upstream of the particulate filter. To achieve appropriate mixing of the injected hydrocarbons with the exhaust stream, a separate hydrocarbon mixer is often provided between the injection location and the particulate filter.
The inventors herein have recognized that when an injector is located in a high temperature environment such as an exhaust system, excessive heating of the injector can cause coking at the injector tip, injector degradation, and/or other component malfunction. Additionally, providing a separate hydrocarbon mixer in the exhaust system increases the required packaging space and design complexity of the system, while also increasing the overall backpressure experienced by the engine.